There’s a riptide running in American politics, and with his State of the Union address, President Barack Obama has an opportunity to turn it in his favor.

As fishermen and other seafarers know, riptides mark a powerful moment of change. The waters look chaotic. But riptides are pregnant with potential for the future. On the surface, the current flows one way — in the old direction. But in the depths below, larger and more decisive currents are running in the opposite direction, a new direction.

The prevailing current since 2010 has been the radical anti-government, anti-tax tide of the tea party that has repeatedly forced gridlock and often brought government to a halt. Just a year ago, with the tea party riding high, pundits predicted the GOP would win the White House and take control of the Senate.

Then came the counter-currents. Obama won a surprisingly convincing reelection, and the Democrats not only kept control of the Senate but added two seats to their majority. In House elections, too, Democrats won more popular votes nationwide than Republicans. Only egregious gerrymandering of congressional districts gave Republicans a 33-vote House majority.

American history, which moves in cycles, may be on Obama’s side. Every 30 or 40 years, the pendulum of our politics swings from an era of conservatism to progressivism or vice versa, and our current conservative era is already 35 years old.

Consider history: The conservative Roaring Twenties gave way to Franklin Roosevelt’s New Deal in 1933. There followed a long progressive era of governmental activism, expanding the social safety net and regulating the excesses of American capitalism. Through the 1950s and ’60s and into the ’70s, mass movements for civil rights, consumer rights, labor rights, women’s rights and environmental protections pushed Washington to expand government, even under Republican President Richard Nixon.

But the tide turned in 1978. The surprise was that our current era of conservatism was ushered in by Democrats under intense pressure from a newly awakened and organized army of business lobbies. For more than three decades, from Jimmy Carter’s presidency through Ronald Reagan and George W. Bush, Congress has largely done the bidding of business. It has cut taxes, rolled back government regulations and delivered many concessions to Wall Street banks and corporate America.

On Capitol Hill, tea party Republicans might still hope that tide remains, but other Republicans see an ebb tide and worry that the GOP is in danger of putting itself on the wrong side of history.

Among voters in 2012, Republicans fared poorly with minorities and women, whomake up growing parts of the electorate. The GOP stronghold was older white men, a shrinking portion of the population. “The demographic changes in America are real, and they are a wake-up call for the Republican Party,” warned former GOP Chairman Haley Barbour.

The policy undercurrents have been shifting, too. Obama’s health care reform marked the first major expansion of the federal safety net since Medicare in 1965. His tax increase on the wealthy last month is the first in decades to target the top 1 percent. The 2010 bank regulatory reform, with its new Consumer Financial Protection Bureau, is the first strong consumer measure since the 1970s.

But Obama’s most daring step, the one with the most far-reaching potential for American politics, is his inaugural call for a populist political crusade, his powerful mantra: “We the People. … We the People … must act now.”

The president is not just out to pass a few bills. He is out to alter the balance of power in Washington, where for 35 years, pro-business and special-interest lobbyists have captured the government. Obama’s gambit is to turn the tide by reviving the people power of the 1950s, ’60s and ’70s.

“You can’t change Washington from the inside. You can only change it from the outside,” Obama declared last fall. “Change happens because the American people demand it, because they rise up and insist on new ideas and new leadership, a new politics for a new time.”

Few took Obama seriously back then, but with his inaugural address, the president laid down his marker. He upped the ante by committing his formidable campaign team, led by Jim Messina, to the goal of converting Middle America’s discontent into political power.

In his State of the Union, the president now has to show that he means business. It’s a big gamble given the political inertia among average Americans. But if Obama can actually stir up a grass-roots populist crusade, the impact will go far beyond the outcome on a few specific issues. The rise of populist activism could transform the dynamics of power in Washington and like a riptide, sweep the nation into a new progressive era.

Hedrick Smith is former Washington bureau chief of The New York Times and author of “Who Stole the American Dream?”